The following slides highlight a report on presentations from the Late-Breaking Clinical Trial Sessions and a Satellite Symposium at the 76th Annual Scientific Session of The American Heart Association held in Orlando, Florida on November 12, 2003. The presentations were originally given by Steven E. Nissen, MD and Allen J. Taylor, MD, and they were reported and discussed by Howard Leong-Poi, MD in a Cardiology Scientific Update. Numerous randomized trials of lipid-lowering therapy have demonstrated that 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors, or statins, reduce the risk of cardiovascular (CV) death, myocardial infarction (MI), stroke, and other CV events among individuals with established coronary artery disease (CAD) and overt hypercholesterolemia. While standard treatment guidelines have recommended a target low-density lipoprotein cholesterol (LDL-C) of < 2.6 mmol/L for secondary prevention of CV events, growing evidence suggests that aggressive lipid-lowering by statin therapy may result in clinical benefits even at LDL-C concentrations far below target levels. Specifically, it has been postulated that newer synthetic statins, which have more potent lipid-lowering effects than 1st generation natural statins, may lead to greater CV protective effects due to more aggressive LDL-C reduction. The issue of Cardiology Scientific Update reviewed the clinical data supporting more aggressive LDL-C lowering for secondary prevention in patients with established CV disease, including late-breaking results of the Reversing Atherosclerosis with Aggressive Lipid Lowering (REVERSAL) study.

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality in Canada and in most industrialized countries. Elevated total and LDL cholesterol are well-recognized risk factors for CVD, and their reduction is associated with important clinical sequelae. Largely on the basis of benefits demonstrated by statins in lipid-lowering trials, the National Cholesterol Education Program (NCEP) Adult Treatment Panel (ATP) III guidelines have recommended that high-risk individuals with a 10-year risk >20% (eg, established CAD, or other CAD risk equivalent such as type II diabetes) should be treated to a target LDL-C concentration of <2.6 mmol/L (secondary prevention). When data from large secondary prevention trials of statin therapy are pooled, the incidence of cardiovascular events over a wide range of achieved LDL-C levels can be further examined, as shown in the above slide. On examining the results of these landmark statin trials, a linear relation between CV events and LDL-C levels is observed, similar to that found in previous observational studies. These results suggest that a threshold LDL-C below which further reduction fails to produce additional benefits in vascular risk reduction has not yet been defined, and may not even exist. If true, the implications are that adherence to current guidelines may potentially lead to inadequate treatment of at-risk patients who may still derive benefit from statin therapy.

The REVERSAL study was a prospective, multicentre, double-blind, randomized trial designed to compare the effects of an aggressive lipid-lowering regimen (atorvastatin 80 mg a day) and a moderate lipid-lowering regimen (pravastatin 40 mg a day), on coronary atheroma burden, as measured by intravascular ultrasound (IVUS). The study design of REVERSAL is summarized in the above slide. Patients with symptomatic CAD, ≥20% stenosis by angiography, and LDL-C concentrations between 3.2 mmol/L and 5.4 mmol/L after an 8-week washout period (off statin therapy), were eligible for entry into the study. The main exclusion criteria was the presence of >50% stenosis of the left main coronary artery. A total of 654 patients in 34 hospitals across the United States were enrolled in the study between June 1999 and September 2001. Patients were randomized to receive pravastatin 40 mg daily or atorvastatin 80 mg daily for 18 months. The rationale for using pravastatin 40 mg was: • it was the highest dose approved for this drug at the start of this trial • it was proven clinically beneficial for the secondary prevention of CAD • it was approved in the United States for slowing progression of atherosclerosis. Atorvastatin was chosen because it was the most potent lipid-lowering agent available and was effective in reducing LDL-C levels to below existing guidelines.

Of the 654 patients enrolled, 502 completed the trial, 249 on pravastatin and 253 on atorvastatin. The main reason for withdrawal was a reluctance to undergo a repeat cardiac catheterization during the follow-up period. Baseline characteristics were well-matched between the 2 treatment groups, as seen in the above slide. The mean age was 56 years, 70% were male, and 20% were diabetic. Baseline LDL-C was 3.9 mmol/L in both treatment groups.

The above slide shows the lipid values at the end of the study period along with the percent changes in the respective lipid values. After 18 months, patients receiving atorvastatin had significantly lower LDL-C levels compared to those on pravastatin (2.0 ± 0.8 mmol/L vs 2.8 ± 0.7 mmol/L respectively, p<0.0001). Treatment with atorvastatin resulted in a mean LDL-C (2.0 mmol/L) well below the target level set by current guidelines. Atorvastatin treatment also resulted in significantly lower triglyceride levels compared to pravastatin treatment. There was a slight nonsignificant increase in high-density lipoprotein (HDL) cholesterol in the pravastatin-treated group compared to the atorvastatin-treated group.

The primary pre-specified endpoint of the study was percent change in intravascular ultrasound (IVUS)-determined atheroma volume. Results of the primary study endpoint are shown in the above slide. While percent change in atheroma volume was unchanged by atorvastatin (0.4% decrease), atheroma volume was seen to increase significantly (2.7% increase) in the pravastatin arm. IVUS was performed during baseline cardiac catheterization and at study completion. A core laboratory at The Cleveland Clinic, blinded to treatment assignment, performed all IVUS measurements. IVUS is a modality used for imaging atherosclerotic plaque, performed via a 1 mm high frequency (30 MHz) ultrasound catheter positioned within the lumen of a vessel. The catheter rotates at 1800 revolutions per minute, allowing real-time imaging of plaques within the wall of the coronary artery. The cross-sectional area of atherosclerotic plaque is then measured in a single slice by planimetry. A motor-drive device performs a standardized pullback of the ultrasound catheter at 0.5 mm per second and, at every mm along the vessel, another cross-sectional slice is obtained. The atheroma volume of the ‘target’ coronary artery between 2 fixed points is then calculated, based on the plaque area at each mm section of the coronary artery imaged (Simpson’s rule). All patients underwent IVUS through a 30 mm or longer length of single ‘target’ coronary artery.

Secondary endpoints included absolute change in total coronary atheroma volume, change in percent obstructive volume, and change in C- reactive protein (CRP) levels on treatment. Results of the secondary endpoints are summarized in the following slides. Similar to the primary endpoint, there was no significant change in total atheroma volume and percent obstructive volume with atorvastatin treatment, while there was significant progression of both in patients on pravastatin, as shown in the above slides.

Both treatment arms showed significant reductions in CRP levels, with significantly greater reductions noted in the atorvastatin arm compared to the pravastatin arm, as seen in the above slide. These differences in the primary and secondary IVUS endpoints between treatment groups were consistent across the 22 pre-specified subgroups. The only exception was in patients without hypertension, where little progression was seen in either treatment arm. The results were also consistent among patients with LDL-cholesterol and CRP levels above and below mean values. In the pravastatin group, progression of atherosclerosis was still seen even when lower LDL-C levels were achieved.

A post hoc analysis was performed on the subset of the 167 patients treated with pravastatin who reached target LDL-C of < 2.6 mmol/L (as per NCEP ATP III guidelines). The results are shown in the above slide. In this subgroup of the pravastatin arm, there was significant atherosclerosis progression by IVUS, despite LDL-C mean values of 2.2 mmol/L.

In the safety data on the high-dose statin therapy used in this study, there were no significant differences in adverse events between the 2 treatment groups, with no differences in AST, ALT, or CK levels between treatment groups, as shown in the above slide. No patients experienced clinical myositis/myopathy. The principle findings of the REVERSAL study are that a more aggressive lipid-lowering regimen using atorvastatin had greater beneficial effects on IVUS-determined coronary atheroma burden compared to a more modest lipid-lowering regimen with pravastatin. This was achieved without significant increases in adverse events, particularly myositis. The results are consistent with those of the ARBITER study (Taylor AJ, et al. Circulation 2002;106:2055-2060) that used identical treatment arms, with similar beneficial effects on carotid atherosclerosis measured by carotid intima-media thickness (CIMT). While REVERSAL was not powered to assess differences in clinical events, these results using a surrogate endpoint raise the possibility that reduction in LDL-C levels to <2.6 mmol/L may lead to additional cardiovascular benefits in patients with symptomatic CAD. While previous studies have demonstrated a consistent relationship between atherosclerosis progression rates and major cardiovascular events, the impact of stopping atherosclerosis progression by aggressive lipid-lowering demonstrated in the REVERSAL study needs to be confirmed by similarly designed comparative statin trials with hard clinical endpoints.